Telescopes from the Ground Up

1923: Other galaxies exist

In the early 1900s, astronomers were debating the makeup of spiral nebulae — cloudy, spiral-shaped objects found throughout the night sky. Were they gas clouds located within our Milky Way galaxy, or were they vast groups of stars located far beyond our galaxy?

In 1919, American astronomer Edwin Hubble tackled the question. His keen astronomical knowledge was combined with a powerful tool – the Hooker telescope with its 100-inch mirror, on top of Mount Wilson in California. Hubble used the telescope’s resolution and light-gathering power to take a series of photographs of the great nebula in Andromeda. For the first time, the images revealed faint stars in the nebula.

Hubble now knew the Andromeda nebula was a collection of stars, but how far away was it? To find out, he used a known method for calculating distance based on very bright variable stars.

A galaxy far, far away

In 1923, Hubble found dozens of these variable stars in Andromeda, and determined their distance. He calculated that Andromeda must be at least 10 times farther away than the farthest stars in the Milky Way. The Andromeda nebula was really the Andromeda galaxy. This discovery implied that the other, even fainter, spirals were probably also galaxies even farther away.

Hubble published his work in 1929 and changed forever our view of the universe. Astronomers no longer thought our galaxy was the entire universe. Now they knew that the universe was composed of many, many galaxies.

Seven decades later, a telescope named in Hubble’s honor helped discover that the observable universe was truly vast, and contained nearly 100 billion galaxies.

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